Faculty of Biological Sciences

Research Bulletin

Organic farming shows limited benefit to wildlife

5th May 2010

Organic farms may be seen as wildlife friendly, but the benefits to birds, bees and butterflies don't compensate for the lower yields produced.

Organic farming shows limited benefit to wildlife [A]
Organic farms may be seen as wildlife friendly, but the benefits to birds, bees and butterflies don't compensate for the lower yields produced, according to new research from the University of Leeds [B].

In the most detailed, like-for-like comparisons of organic and conventional farming to date [C], researchers from Leeds' Faculty of Biological Science found that the benefits to wildlife and increases in biodiversity from organic farming are much lower than previously thought - averaging just over 12 per cent more than conventional farming. [D]

The organic farms in the study produced less than half of the yield [E] of their conventional counterparts, so the research - published online today in Ecology Letters - raises serious questions about how we can use agricultural land to maximise food production and still protect our wildlife [F].

"Over the next forty years, we're going to have to double food production worldwide to keep pace with population increases," [G] says Professor Tim Benton, who led the project. "Our results show that to produce the same amount of food in the UK using organic rather than conventional means, we'd need to use twice the amount of land for agriculture. [H]

"As the biodiversity benefits of organic farming are small, then the lower yield may be a luxury we can't afford, particularly in the more productive areas of the UK. " [I]

Organic farms have come out well in earlier research into biodiversity and wildlife, but as these farms tend to be found in areas with smaller fields, more hedges and woodland, they start with an advantage [J]. The Leeds project, funded under the Rural Economy Land Use programme, aimed to see if organic farming was still as good for wildlife if these landscape effects were taken out of the equation.
The research looked at two areas in Central South West England and the North Midlands, taking into account over 30 variables covering climate, topography, socio-economic conditions, land use and soil type. Thirty-two organic and non-organic farms were paired together, some in 'hotspot' regions with many organic farms and others in 'coldspots' with very few, to help identify any cumulative impacts over a wider area. Comparisons were made also between individual fields, with 192 fields sampled in all. The research looked at birds, insects (including butterflies, bees and hoverflies), earthworms and plants.

Comparing farm by farm, the researchers found a 55 per cent drop in yield compared to a 12.4 per cent increase in biodiversity. However, comparisons between larger areas found that 'hotspots' with a greater density of organic farming showed a 9.1 per cent increase in biodiversity across the board. [K]
"If one field is managed organically without use of herbicides, that can benefit plant species in a field by field comparison, but it won't affect enough of an area to impact on pollinating insects, for example," explains co-researcher on the project, Dr Doreen Gabriel. "However, if you aggregate organic farms together, the benefits can be seen across a wider range of species. "

The research also threw up some unforeseen negative impacts. Conventional farms in 'hotspots' tended to use higher levels of herbicides than those in 'coldspots' to counteract the seeds coming across from their more weed-tolerant neighbours [L]. And numbers of small farmland birds were actually lower on organic farms, as these tend to attract birds such as magpies and jays, which prey on smaller birds [M].

"Organic methods may be a useful part of the land management mix for the less productive parts of the UK, particularly if policies can encourage farmers to coordinate activities to maximise the benefit to wildlife across a larger area [N],"says Professor Benton.

"However, given the lower yield and the limited biodiversity benefit of organic farming, it isn't sustainable to promote it as the best or only method of agriculture [O]. To meet future demands of food production, we will need to keep farming our most productive areas in the most intensive way we can - and potentially offset that by managing some of our remaining land exclusively as wildlife reserves. [P]"

New footnotes and clarifications added 18th May 2010
[A] The views in this press release are based on research published in the Ecology Letters' paper on 5th May plus some conclusions based on a forthcoming paper (see note B) and it also contains context and interpretation by the lead authors on the Ecology Letters' paper of 5th May. The research highlighted in this press release arises from the "ecology" workpackage of larger project, RELU SCALES, and this workpackage involved Leeds' staff Prof Tim Benton, with Prof Bill Kunin and Dr Steve Sait, and the researcher responsible for the execution of the work was Dr Doreen Gabriel. The wider RELU SCALES project is led by Prof Sigrid Stagl based at the Vienna University of Economics and Business, and involves a wide range of investigators from many backgrounds and institutions (ecological farming experts, farm economists, sociologists, hydrologists, soil scientists, philosophers, environmental and ecological economists from the Universities Cambridge, Manchester, Cranfield, Aberdeen, Vienna (Austria), Macaulay Land Use Research Institute, Organic Research Centre Elm Farm and Henry Doubleday Research Association). The conclusions expressed here, particularly regarding the forthcoming work and its implications, do not necessarily represent the views of the RELU-SCALES team, nor the view of the research partner Henry Doubleday Research Association (working name Garden Organic).

[B] This conclusion arises from the paper published 5th May in Ecology Letters, which highlights how biodiversity differs between cereal fields farmed organically or conventionally, and a forthcoming paper, which has been peer-reviewed, which looks at a measure of biodiversity assessed in nature reserves, organic and conventional fields and models the optimal strategy to maximise both yield of crop and biodiversity. The theoretical framework for the forthcoming paper is Green et al (2005) "Farming and the fate of wild nature" vol 305, p550). Green et al. 's argument is that the optimal approach to conserve biodiversity and maximise yield depends on the way farming intensity impacts biodiversity. If farming at lower intensity increases biodiversity, but reduces yield, more land will be required to make up the lost yield, and conversion of the extra land to farming will also have an impact on biodiversity. Thus the optimal strategy for farming yield and maximising biodiversity depends on on (a) the relationship between yield loss and biodiversity gain and (b) the biodiversity in the "extra land" that would be converted to agriculture and thus the "cost" associated with that. If reducing intensity has a large impact in yield but only creates a small increase in biodiversity, farming intensively on some land and managing the "spare land" for biodiversity is the optimal strategy (see Green et al 2005 for details). Conversely, if reducing farming intensity has a big effect on biodiversity but a small impact on yield, farming the whole area extensively is the optimal strategy. This "land sparing vs land sharing" modelling is examined in detail in the forthcoming paper. The current Ecology Letters' paper examines in detail the biodiversity changes and provides (in Table 1) the relative yields in the organic vs. conventional winter cereal fields. It is within the framework of the land sparing vs. land sharing optimal argument that the statement "increase in biodiversity does not compensate for the reduction in yield" is made. This modelling framework can be criticised (for example, it assumes the elasticity of demand is zero) and is conceptually simplistic. However, the conceptual point is if a certain yield is demanded, farming in a way that reduces yield necessitates more land to produce the yield, and the cost of this can be balanced against the benefits.

[C] The May 5th Ecology Letters' paper notes the following caveat. Our design looked at farms matched as closely as possible (in size, enterprise and environment). This was so we could look directly at a like-for-like comparison "controlling" for effects to do with farm size, location and field size etc. This means that, whilst our organic farms are probably fairly representative, our sample of conventional farms is probably not typical (in that our sampled conventional farms are generally smaller than average and mixed rather than either entirely grazing or entirely arable). By the nature of organic practice, it was not possible to find a sample of organic farms that could be matched to very large, arable-only, conventional farms. Thus our research measures the effects of being organic per se, unalloyed with the correlated effects of mixed farming, or of the specific environments in which organic farms tend to be placed (see Gabriel et al. "The spatial aggregation of organic farming in England and its underlying environmental correlates". J. Appl. Ecol. , 46, 323-333). The biodiversity benefits of organic practice thus measured are likely to be smaller than the average biodiversity difference between existing conventional and organic farms. Ours, however, is the best measure of the net biodiversity effect of a (mixed) conventional farm switching to organic, but keeping the rest of its farm practices constant.

[D] Our data show that organic farming on average provides an increase in biodiversity (though the effect depends on both the spatial scale and the taxon). The published literature is very variable in the past about how organic farming may benefit biodiversity (see Hole et al 2003 "Does organic farming benefit biodiversity?" Biological Conservation 122 (2005) 113-130 for a review). Some attempts have been made to synthesise this literature (e.g. Bengtsson et al 2005 "The effects of organic agriculture on biodiversity and abundance: a meta-analysis" J appl ecol 42, 261) which suggest that the "average" effect size is 30-40%.

[E] This statement needs clarifying. What we show, both here and in an additional paper in preparation, is that the winter cereal fields (3 per farm) on average produce 44% the yield of comparable conventional fields. These data come from sampling cereal stems within the field using standardised methodology and drying the grain. The data (in tonnes per ha) are not directly comparable with the yield a farmer would measure (for example, it doesn't include losses during harvesting and transport). These are also not "whole farm" outputs. Clearly, different crops will give rise to different yield estimates and the figure of 44% does not represent all organic crops in all locations. Additionally, we are aware that winter cereals on organic farms are often grown as fodder crops and not for human consumption. Nonetheless, cereals are Europe's most common crop and they were grown on all our farms, and our estimates of yield are correlated with estimates gained in other ways (such as through farmer questionnaires), and additionally have low variance, suggesting they are precise. Furthermore, even with "unmatched farms/fields" comparisons, and for a range of different crops, across Europe organic yields are typically considerably lower than conventional yields (see e.g. Offerman & Nieberg (2002) "Does organic farming have a future in Europe?"EuroChoices 1, 12 - 17).

[F] Managing biodiversity is important for a number of reasons. There is a "non utility" stewardship argument and various utility-based arguments because biodiversity often provides crucial ecosystem services (such as pollination, pest control, soil fertility) that contribute to yields. It is therefore imperative that farming has the minimum impact on biodiversity whilst producing harvestable yield. The key questions is how best to both manage biodiversity and also meet the demands for food (see [A]). There is a broad ecological literature that engages with the question of the ecological impacts of increasing agricultural demand and the land pressure that eventuates (e.g. Tilman et al, 2001, "Forecasting agriculturally driven global environmental change" Science 292, 581; Tilman et al "Agricultural sustainability and intensive production practice" Nature, 418, 671-677 (2002); Green et al op cit; Godfray et al 2010 "Food security: the challenge of feeding 9 billion people" Science 327, 812). This paper, and the forthcoming work, contribute to this debate: food production (whether organic or conventional) impacts biodiversity and ecosystem services. The best solution to managing food and wildlife is both place- and scale-dependent and depends on many factors, including those outlined in [A].

[G] This figure is widely used in the scientific literature (e.g. World Bank, World Development Report 2008: Agriculture for Development (World Bank, Washington, DC, 2008); Royal Society of London, Reaping the Benefits: Science and the Sustainable Intensification of Global Agriculture (Royal Society, London, 2009); Godfray et al 2010 op cit; Tilman et al 2002 op cit). It is also used by the UK Govt in its planning (see footnotes in the Soil Association's report "The Big Fat Lie" available at http://www.soilassociation.org). The Soil Association's report takes issue with the need to double food production worldwide by 2050. Clearly this projected demand is based on many assumptions (both in terms of human population growth and the way a population's demand for food may change) and if the assumptions are changed different projections will be possible. If the world ate less meat, it is certainly true, global demand will go down; but it is a common pattern in international development that as countries develop the demand for meat increases, so food demand often grows at a factor much greater than population growth (e.g. see Delgardo 2003. "Rising consumption of meat and milk in developing countries has created a new food revolution. " J. Nutr. 2003;133, 3907S-3910S). Moreover, even the more modest estimates of increased food demand (by the Environment, Food & Rural Affairs committee in their report: "Securing food supplies up to 2050: the challenges faced by the UK"), cited by the Soil Association in its report anticipates the need for a 70% increase in food production by 2050, and thus a substantial increase in demand for agricultural land.

[H] This is strictly incorrect in that we showed that, on the fields we measured, the wheat yields were about half. This is not the same as the farms producing "half the food" as we did not measure the amount of food produced by each farm and there is not likely to be a one-to-one correspondence between field yield and a farm's food production. Nonetheless, our estimate of yield was about half that on organic fields vs conventional fields, and therefore to produce the same yield the organic area would need to be twice that of the conventional area, at least with regards to production of this grain.

[I] "a luxury we can't afford" was a shortening of "a luxury we, as a society, can't afford". This statement is a value judgement based on a subjective assessment of the global valuation of food vs biodiversity. If food demand is as predicted to be (see [G]) then this presents a very serious challenge that will be difficult to realise (Godfray et al 2010, op cit; Beddington 2010 "Food security: contributions from science to a new and greener revolution" Phil Trans Roy Soc 365:61). If the future demand for food is greater than the supply, it is likely that the value of food will increase relative to the perceived value of biodiversity. This may well lead to productive areas being used for high production rather than conservation.

[K] In other words: organic farming is on average good for biodiversity, and areas where organic farms are common are even better for biodiversity. As the paper indicates, the rank order of "biodiversity yield" is Hotspot organic> Coldspot organic >= Hotspot conventional >coldspot conventional. i.e. a conventional farm in an "organic landscape" can have the same biodiversity as an isolated organic farm in a conventional landscape.

[L] Other explanations are possible for this pattern: for example, conventional farmers in hotspots may receive advice to spray more without there actually being a greater seed rain in the neighbourhood. However, there is ecological literature that suggests that the seed rain hypothesis is a highly plausible one as greater landscape-level weed diversity is associated with greater seed dispersal impacting on within-field diversity (e.g Roschewitz, I. , Gabriel, D. , Tscharntke, T. & Thies, C. (2005). "The effects of landscape complexity on arable weed species diversity in organic and conventional farming". J. Appl. Ecol. , 42, 873-882. ; Valone, T.J. , Hoffman, C.D. , 2002. "Effects of regional pool size on local diversity in small-scale annual plant communities". Ecol. Lett. 5, 477-480. ; Zobel, M. (1997). "The relative role of species pools in determining plant species richness. An alternative explanation of species coexistence?". Trends Ecol. Evol. , 12, 266-269).

[M] See the Ecology Letters' online appendix for some supporting information for this hypothesis and also Dunn et al (forthcoming) "Fear for the family has negative consequences: indirect effects of predators on chick growth in a farmland bird. " J appl Ecol.

[N] Our results indicate that biodiversity often responds to land management at a scale larger than the farm, so managing landscapes pays a biodiversity dividend; and so, in those situations where organic farming is the optimal solution to maximising yield and biodiversity, grouping organic farms together is beneficial. Furthermore, the landscape level effects suggest, as discussed in the Ecology Letters' paper, that any agri-environment scheme would gain dividends if co-ordinated at a landscape level

[O] If farming is to move to increased "low carbon" methodologies, it is likely that the difference between what is regarded as "organic" and what is regarded as "conventional" methodologies will reduce. Low (synthetic) input farming, and organic farming within this, has a necessary role in future food production, in the EU and globally. However, it will be difficult to meet the global demand for food without producing yields that are, on average, at the equivalent, or greater, levels of productivity than current conventional (Beddington, 2010 op cit) or without vastly increasing the area of land under agriculture, with its concomitant environmental cost. The maximum global increase in agricultural area that can be attained (including taking in the area under current rainforest) is 2.16x the current area (Fischer, G. , van Velthuizen, H.T. & Nachtergaele, F.O. (2000) "Global agroecological zones assessment: methodology and results". IIASA Interim Report IR-00-064. International Institute for Applied Systems Analysis, Vienna, Austria. http://www.iiasa.ac.at/Admin/PUB/Documents/IR-00-064.pdf. ) suggesting that if we need to double food production by mid century (see [G]) whilst at the same time losing yield to climate change (e.g. Lobell, D.B. , Burke, M.B. , Tebaldi, C. , Mastrandrea, M.D. , Falcon, W.P. &Naylor, R.L. (2008) "Prioritizing climate change adaptation needs for food security in 2030". Science, 319, 607-610. ) there will be extreme land pressure (Tilman et al 2001; Godfray et al 2010; Gabriel et al 2009). The need to ensure high outputs from existing agricultural land will therefore most likely intensify (Beddington 2010 op cit).

[P] The statement does not necessarily refer to a conceptual separation of biodiversity into different regions and farming into other regions (i.e. a "two tier countryside" as it has been suggested in the press). Biodiversity plays important roles in natural enemy suppression and pollination etc, so it is likely that it will always be beneficial to encourage biodiversity whether the landscape is conventionally or organically farmed (and this need is likely to increase with the development of low farming methodologies). Intensively farmed landscapes can however still be wildlife-sympathetic in terms of marginal management and the management of non-cropped areas. It is likely however, that there will remain the necessity to farm in a way to maximise yield. Under current conventional agriculture, this may equate to intensively managed field areas with wildlife-friendly field margins and non-cropped areas. In such a landscape, specific areas set aside for management of biodiversity ("nature reserves" or areas managed to promote biodiversity within fields/farms) coupled with the existing biodiversity on the conventional farms, will preserve the optimum biodiversity whilst producing the required yield.